Use cargo generate-lockfile to update JikesRVM's Cargo.lock

[qinsoon]

auto-merge.yml uses cargo build to generate lockfile for most bindings. But this does not work for JikesRVM:

1. JikesRVM uses --target i686-unknown-linux-gnu which is not installed automatically when running cargo build.
2. JikesRVM's cargo project uses some Rust source files that are generated during building JikesRVM. So we cannot build the cargo project alone from a fresh repo clone. We have to do a full build.

As a workaround, we use cargo generate-lockfile for JikesRVM. cargo generate-lockfile will update the version of dependencies. But we do not have a better option for JikesRVM

[qinsoon]

The previous auto-merge.yml failed for JikesRVM: https://github.com/mmtk/mmtk-core/actions/runs/6621479194/job/17985509918

[wks]

LGTM